Sure. But for most people (even fairly technical people!), that doesn't actually provide any advantage. If one lacks the skills to fix the software, the fact that they have the ability to do so doesn't give them any benefit.
You can fix your own software but it is not at all guaranteed that there is anyone else interested in fixing your particular problem to anything like the level of closed-source OSs.
Closed source OSes like MS Windows and OSX dont permit you to see, let alone fix things internally.